It is quite common for researchers to present their research work at a conference and submit it to a journal as well. Researchers often first publish a paper and then promote it at several conferences. If you wish to present your published paper at a conference, you can first write to the editor of the journal to find out if it’s acceptable to do so. The journal’s response depends on whether the copyright was transferred at the time of acceptance. The journal might allow you to present only an overview or an excerpt of the findings and not the whole paper.
Once you get permission from the journal, you can proceed with the conference presentation. But do mention in your cover letter that your paper has been published in X journal along with the publication date. And if your paper is accepted at the conference, your presentation/poster must include a footnote reiterating the same information.
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